One of the trickier decisions in a Montessori inventory sounds ridiculously small: what number goes on the material? I like to start at the beginning of a subject area and work along the shelves. But I also know what happens when you finish numbering and then discover another set tucked away in a box. I don't want to renumber half a school because we found one missing piece of the puzzle. So I keep two things separate: the inventory number identifies the material; the recorded shelf location tells us where it belongs in the sequence. When another set turns up, it gets the next available inventory number. It can still go between two earlier-numbered materials on the shelf. I do the same with completeness. “Complete,” “incomplete,” and “unknown” mean different things. And a complete set might still need laminating, so that goes in the notes. This is exactly the kind of detail I wanted the spreadsheet to handle when I designed it. Schools can use it independently, while consulting a trained guide or the relevant references for materials they need help identifying. Here's the Lower Elementary version: https://www.teacherspayteachers.com/Product/AMS-Aligned-Montessori-Materials-Inventory-Lower-Elementary-17834885